1. Field of the Invention
The present invention relates generally to data processors using CPUs capable of processing one instruction in one clock cycle as represented by RISC type CPUs and data processing methods thereof and, more particularly, to an inexpensive data processor with higher processing speed and a data processing method thereof.
2. Description of the Related Art
In general, a page printer analyzes print data or control data applied from a host, then processes the analyzed data as a bit image into a bit-map memory and prints the processed image data on paper by a printer engine.
In order to process the data from the host into the bit image, a printer controller (data processor) is employed, the processing speed of which greatly affects the throughput of the entire printer.
In recent years, a page printer that employs PDL (Page Description Language) such as Postscript as control language has rapidly been popular. This PDL printer can enlarge or rotate characters very easily as compared to a PCL printer using PCL (Printer Control language); however, it takes time to process data into a bit image, resulting in two great disadvantages, a lower output speed and a higher cost.
For further propagation of the PDL printer, a low-cost printer controller with higher processing speed must be developed in the future.
A CISC (Complex Instruction Set Computer) type CPU such as a 68020 processor manufactured by Motorola Inc. for example, is used in a printer controller of a conventional PDL printer.
While the CISC type CPU achieves an efficient execution of a high level language since a set of complicated instructions are added, it requires at least three clock cycles for processing one instruction and hence takes a considerable time to process data into a bit image.
For example, it takes approximately 80 seconds to describe an image for an evaluation test that includes both text and images, called "Ventura Scoop" in Postscript and then process data thereof into a bit image. An output time for the page printer is a total time that file transfer time and paper conveying time are added to this process time.
Since the throughput of the printer engine is usually about 4 to 40 (sheets/min), the process time of 80 seconds required to process the data into the bit image is too long even for a lower-speed printer engine.
Thus, a conventional printer controller (data processor) must achieve higher clock frequencies in order to increase the processing speed. If the higher clock frequencies are achieved, SRAMs that operate at a higher speed but are expensive must be used as memory devices, and memories that operate at a higher speed should be used also as other peripheral devices. This results in higher costs and other numerous problems to be solved in circuit design.